Progressive image signal transmitter, progressive image signal receiver and, medium

ABSTRACT

There are provided MPEG2 video encoding means  102  for converting a progressive signal to a bitstream  512  in accordance with the format of ISO/IEC 13818-2, flag bit analyzing means  503  for extracting, from the bitstream  512 , data on the frame rate of a material and adaptably specifying a rate doubling method, second MPEG2 video decoding means  504  for receiving the bitstream, reconstructing an image signal from the bitstream, and outputting the progressive signal, and the like, whereby a progressive output conforming to the frame rate of a display system and free from image quality degradation is obtained.

TECHNICAL FIELD

[0001] The present invention relates to a progressive image signaltransmitting apparatus, a progressive image signal receiving apparatus,and a medium each using a bitstream obtained by encoding, e.g., aprogressive video signal (sequential scanning signal) based on the MPEG2formats.

BACKGROUND ART

[0002] In recent years, the international standardization of MPEG2(Moving Picture Experts Group the 17-th phase 2) (registration inISO/IEC 13818-1, 2, 3) has increased the importance of a digitaltransmission/reception system using digital high-efficiency encoding.The use of the MPEG2 encoding scheme has raised expectations for channelmultiplexing, improved user interface, and diversified service based onthe prospect of additional data transmission, while enablingsimultaneous transmission of signals with various image qualities(resolutions) from a single transmitter. As a result, a sequentialscanning signal with high image quality (progressive signal) can betransmitted in digital broadcasting.

[0003] Below, a description will be given to a conventional progressivesignal transmission/reception system.

[0004]FIG. 13 is a block diagram showing the structure of theconventional progressive signal transmitting/receiving apparatus.

[0005] It is to be noted that, in the following description, an imagestructure is expressed by using signs i (interlace) and p (progressive)as abbreviations in order to distinguish whether the image structure isinterlace or progressive and express a frame rate in a comprehensiblemanner. By way of example, a progressive signal at a rate of 24 framesper second may be described as 24p and an interlace signal at a rate of60 frames per second may be described as 60i.

[0006] In FIG. 15, a reference numeral 1301 denotes a viewdiagrammatically showing the structure of a video material recorded at asampling rate of 24 frames per second, which is represented by acinematic film material or the like. A reference numeral 1302 denotes a24p/60i converter for converting a picture at the rate of 24frames/second to a normal NTSC television signal at a rate of 60fields/second. A reference numeral 1303 denotes an MPEG2 video encoderfor encoding the aforesaid signal at the rate of 60 fields/second to abitstream in accordance with the description in ISO 13818-2(MPEG2-Video). A reference numeral 1304 denotes an MPEG2 video decoderfor receiving the aforesaid bitstream and reversely converting thereceived bitstream to the 60i signal at the rate of 60 fields/second. Areference numeral 1305 denotes a double rate converter for doubling thehorizontal scanning rate of the 60i signal.

[0007] A description will be given to the operation of the conventionalprogressive signal transmission/reception system thus structured. Sincethe film material with the rate of 24 frames/second with no alterationnormally requires a special-purpose reproducing device or recordingdevice, it is initially converted to the 60i signal at the rate of 60fields/second, which is mostly stored in a D1 or S-VHS tape afterwardand-distributed.

[0008] The 24p/60i converter 1302 operates to convert the signal at therate of 24 frames/second to a signal at the rate of 60 fields/second byappropriately inserting field repeats in the signal at the rate of 24frames/second.

[0009]FIG. 16 is a view for illustrating the operation of the 24/60iconverter. In FIG. 16, it is assumed that a sign A1 represents a fieldimage consisting of the odd-numbered lines (lines 1, 3, 5, . . . ) of aframe A sampled at a time 0 and a sign A2 represents a field imageconsisting of the even-numbered lines (lines 2, 4, 6, . . . ) of thesame frame A.

[0010] It is also assumed that a sign B1 represents a field imageconsisting of the odd-numbered lines of a frame B sampled at a time 1and a sign B2 represents a field image consisting of the even-numberedlines of the frame B.

[0011] The difference between the sampling times 0 and 1 is {fraction(1/24)} seconds in the case of the film material.

[0012] Likewise, a sign C1 represents a field image consisting of theodd-numbered lines of a frame C at a time 2 and a sign C2 represents afield image consisting of the even-numbered lines of the frame C.

[0013] On the other hand, a sign D1 represents a field image consistingof the odd-numbered lines of a frame D at a time 3 and a sign D2represents a field image consisting of the even-numbered lines of theframe D.

[0014] An example of an output from the 24p/60i converter 1302 is suchan output signal as shown in FIG. 16. Specifically, the 24p/60iconverter 1302 operates to obtain output images (A1, A2), (A1, B2), (B1,C2), (C1, C2), and(D1, D2) having a 5-frame field structure from inputimages A, B, C, D having a 4-frame frame structure by inserting a fieldrepeat in each of the frames A and C. A sign (f1, f2) is assumed toindicate that a pair of fields f1 and f2 constitute one frame. A sign f1represents an image consisting of the odd-numbered lines of the frame,while a sign f2-represents an image consisting of the even-numberedlines thereof. The output signal forms a signal at the rate of 60fields/second.

[0015] The signal at the rate of 60 fields/second is inputted to theMPEG2 video encoder 1303.

[0016] The MPEG2 video encoder 1303 operates to convert the inputtedvideo signal to a bitstream compliant with the format described inISO/IEC 13818-2 and output the bitstream. The bitstream output isconnected to the MPEG2 video decoder 1304 via a transmission system.

[0017] At this time, there are cases where the MPEG2 video encoder 1303encodes the entire frames (30 frames per second) of the inputted signal60i and outputs the encoded frames without any alterations and where theMPEG2 video encoder 1303 detects a field repeat at the encoder side,performs internal processing so as not to transmit the repeated field,and transmits only data at the rate of 24 frames per second.

[0018] In the case where the MPEG video encoder 1303 encodes all theframes of the inputted signal 60i and outputs the encoded frames, theMPEG2 decoder 1304 encodes each frame of the video signal inputtedthereto into a bitstream and outputs the bitstream.

[0019] In the case where the MPEG2 video encoder 1303 detects the fieldrepeat at the encoder side, performs processing so as not to transmitthe repeated field, and transmits only data at the rate of n 24 framesper second, the MPEG2 video encoder 1303 transmits only signalsrepresenting the 4 frames of A, B, C, and D but converts each of thesignals representing the frames A and C to a bitstream in a formobtained by adding 1 to the repeat_first_field flag bit in accordancewith the format described in ISO/IEC 13818-2 and outputs the bitstream.

[0020] The MPEG2 video decoder 1304 receives the bitstream produced inaccordance with the foregoing procedure and performs a reverse operationin accordance with the grammar described in MPEG2 to reconstruct thevideo signal from the bitstream.

[0021] In the case where the MPEG2 video encoder 1303 detects the fieldrepeat in the input signal, performs processing not to transmit therepeated field, and transmits only data at the rate of 24 frames persecond, the MPEG2 video decoder 1304 operates as follows.

[0022] In the case where the repeat_first_field flag is 1 in the inputbitstream, one field of the target frame is repeatedly outputted. In thecase where the repeat_first_field flag is 0, the image signal isoutputted without performing a field repeat.

[0023] Consequently, the output of the MPEG2 video decoder 1304 is thesame signal at the rate of 60 fields/second in either of the cases wherethe entire frames of the input signal 60i are encoded and outputted andthe case where the field repeat is detected at the encoder side,processing is performed not to transmit the repeated field, and onlydata at the rate of 24 frames per second is outputted, resulting in nodifference in terms of frame rate and internally constructed image.

[0024] The rate doubling unit 1305 receives the output of the MPEG2video decoder and transforms the signal at the rate of 60 fields/secondto a signal having a scanning rate double the scanning rate for a linescanning line, i.e., a frame rate of 60 frames/second.

[0025] FIGS. 17(a) and 17(b) are for illustrating inputs and outputs ofthe rate doubling unit 1305. In FIGS. 17(a) and 17(b), it is assumedthat the signs A1, A2, B1, B2, C1, C2, D1, D2, A, B, C, and D representthe same images as represented by the signs in FIG. 16. As a techniquefor rate doubling, there is one implemented by a repeat in a fieldstructure and one implemented by a repeat in a frame structure. FIG.17(a) is for illustrating the case where rate doubling is implemented bya repeat in a field structure. FIG. 17(b) is for illustrating the casewhere rate doubling is implemented by a repeat in a frame structure.

[0026] In the case where rate doubling is implemented by a repeat in afield structure, the field Al which is intrinsically image data for anodd field is also used for an even field, thereby achieving effect thata frame at the sampling time for the field Al is composed of a singlefield, as shown in FIG. 17(a). This enables the obtention of a doublerate signal at the rate of 60 frames/second from a signal at the rate of60 fields/second.

[0027] In the case where rate doubling is implemented by a repeat in aframe structure, the field Al and the field A2 immediately subsequentthereto combine to compose one frame, thereby achieving the effect thatthe same frame as outputted at the sampling time for the field Al isalso outputted at the sampling time for the field A2. This enables theobtention of a double rate signal at the rate of 60 frames/second from asignal at the rate of 60 fields/second.

[0028] In the case shown in FIG. 17(a), however, the foregoingconventional structure presents the problem that, though the temporalorder of display- is A B C D and correct, image quality in the verticaldirection is significantly degraded because the same field data iswritten twice in each of the frame structure.

[0029] In the case shown in FIG. 17(b), the conventional structure alsopresents the problem that image quality is degraded because a framecomposed of a combination of fields not sampled at the same time, suchas (A1, B2) or (B1, C2), is sporadically present and an inter-fielddifference is particularly large in a scene involving a dynamic motionin the direction of a time axis, though image quality is not degraded inthe vertical direction.

DISCLOSURE OF THE INVENTION

[0030] In view of the foregoing conventional problems, it is thereforean object of the present invention to provide a progressive image signaltransmitting apparatus, a progressive image signal receiving apparatus,and a medium each capable of obtaining, even when an inter-field motionis dynamic, a double rate signal superior to that obtainedconventionally and maintaining vertical resolution.

[0031] To attain the object, a first aspect of the present invention(corresponding to the invention defined in claim 1) is a progressiveimage signal receiving apparatus comprising: video decoding means forreceiving a bitstream, converting the bitstream to-an interlaced videosignal and outputting the video signal; frame structure analyzing meansfor calculating, based on respective signals representing a currentframe and a frame which is 1 frame time previous to the current frameeach outputted from the video decoding means, a difference between theboth frame signals and outputting a specified control signal based on aresult of the calculation; and rate doubling means for producing a framesignal based on the video signal outputted from the video decoding meansand on the control signal outputted from the frame structure analyzingmeans to provide a progressive signal at a scanning rate which is aspecified number of times as high as a scanning rate of the outputsignal from the video decoding means.

[0032] A second aspect of the present invention (corresponding to theinvention defined in claim 2) is a progressive image signal receivingapparatus comprising: video decoding means for receiving a bitstream andoutputting an interlaced video signal ; temporary storing means forreceiving the output signal from the video decoding means and delayingthe signal by a 1 frame time; judging means for calculating, based on acurrent signal outputted from the video decoding means and a previousframe signal outputted from the temporary storing means, a differencebetween the both frame signals and outputting a specified control signalbased on a result of the calculation; and rate doubling means forproducing a frame signal based on the video signal outputted from thetemporary storing means and on the control signal outputted from thejudging means to provide a progressive signal at a scanning rate whichis a specified number of times as high as a scanning rate of the outputsignal from the temporary storing means.

[0033] A fifth aspect of the present invention (corresponding to theinvention defined in claim 5) is a progressive image signal receivingapparatus, wherein the frame structure analyzing means calculates, incalculating the difference between the both frame signals, the sum ofthe absolute values of differences between pixels in a part of thecurrent frame and pixels in a part of the previous frame.

[0034] A sixth aspect of the present invention (corresponding to theinvention defined in claim 6) is a progressive image signal receivingapparatus comprising: video decoding means for receiving a bitstream,converting the bitstream to a video signal of progressive type, andoutputting the video signal; and flag bit analyzing means for detecting,in the bitstream, a flag signal indicating the presence or absence of afield repeat described correspondingly to a frame signal and outputting,to the video decoding means, the presence or absence of the field repeatindicated by the detected flag signal, if the output from the flag bitanalyzing means indicates the presence of the field repeat, the videodecoding means repeatedly outputting the same frame signal as the framesignal corresponding to the flag signal and outputting the video signalof progressive type at a scanning rate which is a specified number oftimes as high as a scanning rate of the frame signal in the bitstream.

[0035] A seventh aspect of the present invention (corresponding to theinvention defined in claim 7) is a progressive image signal transmittingapparatus for transmitting a video material shot by a sequentialscanning (progressive scanning) method in accordance with a bitstreamdefined in ISO/IEC 13818-2, the transmitting apparatus describing aframe rate of the video material by using a bit position in a user dataregion in the bitstream and transmitting the frame rate.

[0036] A ninth aspect of the present invention (corresponding to theinvention defined in claim 9) is a progressive image signal receivingapparatus for receiving a bitstream transmitted from a transmittingapparatus and outputting a sequential scanning signal to a progressivemonitor, the receiving apparatus comprising: second flag bit analyzingmeans for recognizing a frame rate of a video material from bit data ata given bit position predefined by agreement with the transmittingapparatus; and video decoding means for receiving an output of thesecond flag bit analyzing means and the bitstream, determining thefrequency of frame repeats based on a ratio between the output of thesecond flag bit analyzing means and a frame rate displayed on theprogressive monitor, reconstructing an image, and outputting aprogressive signal.

[0037] A twelfth aspect of the present invention (corresponding to theinvention defined in claim 12) is a progressive image signal receivingapparatus for receiving a bitstream defined in ISO/IEC 13818-2 andoutputting a progressive signal, the receiving apparatus comprising:flag bit analyzing means for analyzing whether or not a code valuedescribed in a frame_rate_code flag in a sequence_header is half thevalue of a frame rate of the progressive signal outputted and outputtinga result of the analysis as a control signal; video decoding means forreceiving the bitstream and reconstructing an image based on thedefinition in ISO/IEC 13818-2; and rate doubling means for converting,based on the control signal outputted from the flag bit analyzing means,an output signal from the video decoding means to a signal at a scanningrate which is double the scanning rate of the output signal.

[0038] With such structures, it is judged whether or not a decoded frameis a frame to be repeatedly displayed at the receiving apparatus andcontrol operation is performed based on the judgment. This achievesdouble rate display without causing the degradation of image quality.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039]FIG. 1 is a block diagram showing a structure of a progressiveimage signal transmitting/receiving apparatus according to a firstembodiment of the present invention;

[0040]FIG. 2 is a view for illustrating the operation of frame structureanalyzing means according to the first embodiment of the presentinvention;

[0041]FIG. 3 is a view for illustrating the operation of rate doublingmeans according to the first embodiment of the present invention;

[0042]FIG. 4 is a block diagram showing a structure of a progressiveimage signal transmitting/receiving apparatus according to a secondembodiment of the present invention;

[0043]FIG. 5 is a block diagram showing a structure of a progressiveimage signal transmitting/receiving apparatus according to a thirdembodiment of the present invention;

[0044]FIG. 6 is a view for illustrating the operation of flag bitanalyzing means according to the third embodiment of the presentinvention;

[0045]FIG. 7 is a view for illustrating the operation of MPEG2 videodecoding means according to the third embodiment of the presentinvention;

[0046]FIG. 8 is a block diagram showing a structure of a progressiveimage signal transmitting/receiving apparatus according to a fourthembodiment of the present invention;

[0047]FIG. 9 is a view representing the Sequence_header for illustratingthe respective operations of third MPEG video encoding means and theflag bit analyzing means according to the fourth embodiment of thepresent invention;

[0048]FIG. 10 is a view representing the Sequence_extension forillustrating the respective operations of the third MPEG video encodingmeans and the flag bit analyzing means according to the fourthembodiment of the present invention;

[0049]FIG. 11 is a view for illustrating the operation of the MPEG2video decoding means according to the fourth embodiment of the presentinvention;

[0050]FIG. 12 is a view for illustrating the operation of the flag bitanalyzing means according to a fifth embodiment of the presentinvention;

[0051]FIG. 13 is a view for illustrating the operation of the flag bitanalyzing means according to the fifth embodiment of the presentinvention;

[0052]FIG. 14(a) is a view diagrammatically showing a 24p signal in thecase where a material is 24p and an output signal is 50p according toanother embodiment of the present invention;

[0053]FIG. 14(b) is a view diagrammatically showing a 50i signalaccording to the embodiment;

[0054]FIG. 14(c) is a view diagrammatically showing a 50p signalaccording to the embodiment;

[0055]FIG. 15 is a block diagram showing a conventional progressiveimage signal transmitting/receiving apparatus;

[0056]FIG. 16 is a view for illustrating the operation of theconventional progressive image signal transmitting/receiving apparatus;

[0057]FIG. 17(a) is a view for illustrating a repeating operationperformed in a field structure by the conventional progressive imagesignal transmitting/receiving apparatus; and

[0058]FIG. 17(b) is a view for illustrating a repeating operationperformed in a frame structure by the conventional progressive imagesignal transmitting/receiving apparatus.

[0059] (Explanation of Reference Numerals)

[0060]101 24p/60i converting means

[0061]102 MPEG2 video encoding means

[0062]103 MPEG2 video decoding means

[0063]104 frame structure analyzing means

[0064]105 rate doubling means

BEST MODES FOR IMPLEMENTING INVENTION

[0065] Referring now to the drawings, the embodiments of the presentinvention will be described.

[0066] (Embodiment 1)

[0067]FIG. 1 is a block diagram showing the respective structures of areceiving apparatus and a transmitting apparatus as an embodiment of aprogressive image signal receiving apparatus according to the presentinvention.

[0068] By way-of example, the present embodiment will describe the caseof obtaining, from a sequential scanning signal (hereinafter referred toas progressive signal) at a rate of 24 frames per second, a progressivesignal at a rate of 60 frames per second for ease of explanation.

[0069] In FIG. 1, a reference numeral 101 denotes 24P/60i convertingmeans for converting the progressive signal having the rate of 24 framesper second for a film material or the like to an interlace signal havinga field structure with a rate of 60 fields per second. A referencenumeral 102 denotes MPEG video encoding means for producing a bitstreamof an image signal in accordance with the description in ISO/IEC13818-2, while a reference numeral 103 denotes MPEG2 video decodingmeans for reconstructing the image signal at the rate of 60fields/second from the bitstream. A reference numeral 104 denotes framestructure analyzing means for reading frame data from the foregoingvideo decoding means and calculating a difference between the frame dataand data on the previous frame to determine the presence or absence ofthe difference, while a reference numeral 105 denotes rate doublingmeans for receiving an output from the foregoing MPEG2 video decodingmeans 103, adaptably selecting a rate doubling method based on an outputcontrol signal from the frame structure analyzing means 104, convertingan output image signal from the MPEG2 video decoding means 103 to asignal having a doubled scanning rate, and outputting the signal.

[0070] On the other hand, a signal 110 is a 25p signal having a framerate of 24 frames/second and a signal 111 is a 60i signal having a framerate of 60 fields/second. A reference numeral 112 denotes a bitstreamdefined in ISO/IEC 13818-2. A reference numeral 113 denotes areconstructed 60i image signal having a frame rate of 60 fields/second.A reference numeral 114 denotes a 60p image signal having a doubledframe rate of 60 frames/second. A reference numeral 115 denotes acontrol signal notifying the rate doubling means 105 of a rate doublingmethod.

[0071] The rate doubling means 105 according to the present embodimentis obtained by improving the conventional rate doubling converter 1305having the repeating function illustrated in FIG. 17(b). The differencebetween the present embodiment and the conventional embodiment will bedescribed briefly with reference to FIG. 3.

[0072] Specifically, the rate doubling means 105 produces one frameZ1+Z2 by using the fields Z1, Z2 at the time t=2 and is assumed torepeatedly output the same frame Z1+Z2 even at the time t=−1, as shownin FIG. 3.

[0073] Under such circumstances, the rate doubling means 105 accordingto the present embodiment is different from the conventional case inthat it is structured to determine, in generating a frame at the timet=0, whether or not it repeatedly outputs the same frame Z1+Z2 asproduced at the time t=−1 based on the control signal from the framestructure analyzing means 104. A specific operation of the rate doublingmeans 105 will be described later in greater detail.

[0074] The reason that the rate doubling means 105 according to thepresent invention is structured to repeatedly output the same framesignal twice and judge whether or not the same frame signal should beoutputted three times is as follows.

[0075] Since the present embodiment has described the case of obtaininga progressive signal at the rate of 60 frames per second from aprogressive signal at the rate of 24 frames per second, the presentembodiment is based on the assumption that the frame rate becomes60/24=2.5.

[0076] Accordingly, in the case of obtaining a progressive signal at therate of 60 frames per second from a progressive signal at the rate of mframes per second, e.g., the presence or absence of the ([60/m]+1)-threpeat of the frame signal outputted from the rate doubling means 105according to the present embodiment is judged. It is assumed here thatthe sign [n] represents a maximum integer not exceeding n.

[0077]FIG. 3 is a view for illustrating the operation of the ratedoubling means 105. In FIG. 3, the horizontal axis represents timetransition and each of the vertical lines represents an image composedof one field. Here, the difference of a numerical value 1 on the timeaxis corresponds to {fraction (1/60)} seconds.

[0078] A description will be given to the operation of the progressivesignal transmitting/receiving apparatus thus structured. First, the24p/60i converter 101 produces a signal at the rate of 60 fields/secondfrom a material with the rate of 24 frames per second in exactly thesame manner as in the description of the conventional technique.

[0079] That is, the relationship between the 24P signal 110 as an inputsignal and the produced 60i signal 111 at the rate of 60 fields/secondis exactly the same as the relationship between the input image and theoutput image shown in FIG. 16.

[0080] The 60i signal 111 is converted by the MPEG2 video encoder means102 to a bitstream defined in ISO/IEC 13818-2. The bitstream 112 issubjected to arbitrary modulation and demodulation and transmitted toreach the receiver via a transmission path. At the receiver, thebitstream 112 is inputted to the MPEG2 video decoding means 103.

[0081] The MPEG2 video decoding means 103 reconstructs an image signalfrom the bitstream in accordance with the description in ISO/IEC13818-2.

[0082] To judge whether or not the same frame signal should berepeatedly outputted three times, the frame structure analyzing means104 operates to calculate, for each of the fields, the absolute value ofthe difference between the value of each pixel in an image beingcurrently decoded by the video decoding means 103 and the value of thecorresponding pixel in a frame to be displayed 1 frame time previousthereto at the same horizontal and vertical positions and add up thecalculated absolute values to provide a total sum. Briefly, the framestructure analyzing means 104 compares, for each of the mutuallycorresponding fields, the decoded frame outputted from the MPEG2 videodecoding means 103 with the frame to be displayed 1 frame time previousthereto such that the field parities thereof coincide with each otherand performs the following calculations.

[0083]FIG. 2 is a view for illustrating the operation of the framestructure analyzing means 104.

[0084] In FIG. 2, a reference numeral 201 denotes an image frame at thetime t=0. For simplicity, the description will be given, by way ofexample, to the case where one frame is composed of 720 horizontalpixels and 480 vertical lines.

[0085] A reference numeral 202 denotes the value of a brightness signalat a location of the y-th pixel (x is an integer) on the x-th horizontalline (x is an integer). The brightness value is expressed as a sign F(x,y).

[0086] A reference numeral 203 denotes an image frame at the time t=1.The difference between the times 0 and 1 corresponds to a timedifference of {fraction (1/30)} seconds. The brightness value at thelocation x, y in the image frame 203 is represented by G(x, y). At thistime,

[0087] (Numerical Expression 1)$\alpha = {\sum\limits_{x = {{2n} - 1}}^{480}{\sum\limits_{y = m}^{720}{{{F\left( {x,y} \right)} - {G\left( {x,y} \right)}}}}}$

[0088] where n=1, 2 . . . 240, m=1, 2 . . . 720

[0089] (Numerical Expression 2)$\beta = {\sum\limits_{x = {2n}}^{480}{\sum\limits_{y = m}^{720}{{{F\left( {x,y} \right)} - {G\left( {x,y} \right)}}}}}$

[0090] where n=1, 2 . . . 240, m=1, 2 . . . 720

[0091] In the foregoing Numerical Expression 1, a represents the sum ofthe absolute values of the differences between the odd fields. In theforegoing Numerical Expression 2, β represents the sum of the absolutevalues of the differences between the even fields.

[0092] It is assumed that each of α and β is set to a value 0 at thebeginning of a field and evaluated as the sum during the period of oneframe.

[0093] If α or β is smaller than a predetermined threshold value, it isjudged that the corresponding field of a frame currently being decodedis a repeat of the preceding field and it is reported as the controlsignal 115 to the rate doubling means 105 that the corresponding framecontains the repeated field.

[0094] Next, a more specific description will be given to the operationof the rate doubling means 105 with reference to FIG. 3.

[0095] In the drawing, each of Z1, Z2, A1, A2, B1, B2, C1, and C2represents one field image and the notation thereof is similar to thatused in FIGS. 17(a) and 17(b) and the like illustrating the conventionalembodiment.

[0096] For easier recognition of contrast between the output imagesignal from the rate doubling means 105 and the output image signal (seeFIGS. 17(a) and 17(b)) from the conventional rate doubling converter1305 (see FIG. 15), FIG. 3 shows the case where an input signal to therate doubling means 105, which is shown as the 60i image signal 113, isidentical to the 60i signal, which is the input signal shown in FIGS.17(a) and 17(b). In FIG. 3, a portion accompanied by the referencenumeral 113 diagrammatically shows the 60i image signal as the input anda portion accompanied by the reference numeral 114 diagrammaticallyshows the 60p image signal as the output.

[0097] As stated previously, it is assumed that the same frame Z1+Z2 isoutputted at the time t=−2 and at the time t=−1.

[0098] Next, a description will be given to the operation of the ratedoubling means 105 at the time t=0 and thereafter.

[0099] At the time t=0, the frame structure analyzing means 104calculates the sum (corresponding to a in the Numerical Expression (1))of the absolute values of the differences between the field image Z1 atthe time t=−2 and the field image A1 at the time t=0 in FIG. 3. At thistime, the value of a becomes larger than the predetermined thresholdvalue so that the frame structure analyzing means 104 transmits, to therate doubling means 105, the control signal 115 directing thatoutputting not be repeated as an output operation at the time t=0.Consequently, the rate doubling means 105 uses the field image A1 at thetime t=0 as the odd field and the field image A2 at the time t=1 as theeven field to produce A1+A2 as one frame and outputs the frame.

[0100] At the time t=1, the same frame A1+A2 as outputted at the timet=0 is repeatedly outputted unconditionally.

[0101] At the time t=2, the frame structure analyzing means 104calculates the sum (corresponding to a in the Numerical Expression (1))of the absolute values of the differences between the field image A1 atthe time t=2 and the field image A1 at the time t=0. At this time, thevalue of α becomes smaller than the-predetermined threshold value sothat the field image A1 at the time t=2 is judged to be a repeat fieldof the field image A1 at the time t=0 and the control signal 115directing that the frame identical to the preceding frame be repeatedlyoutputted is transmitted to the rate doubling means 105. The ratedoubling means 105 accepts the control signal 115 and repeatedly outputsthe same frame A1+A2 as outputted at the time t=1 as a double rateoutput at the time t=2. It follows therefore that the rate doublingmeans 105 eventually outputs the frame A1+A2 consisting of the fieldimages A1 and A2 three times at the times t=0, 1, 2.

[0102] At the time t=3, the sum (corresponding to β in the NumericalExpression (2)) of the absolute values of the differences between thefield image B2 at the time t=3 and the field image A2 at the time t=1 iscalculated. At this time, since β has a value larger than thepredetermined threshold value, the frame structure analyzing means 104outputs, to the rate doubling means 105, the control signal 115directing that outputting not be repeated as a double rate output at thetime t=3. As a result, the rate doubling means 105 uses the field imageB1 at the time t=4 as the odd field and the field image B2 at the timet=3 as the even field to produce B1+B2 as one frame and outputs theframe.

[0103] At the time T=4, the rate doubling means 105 repeatedly outputsthe same frame as the output frame B1+B2 at the time t=3.

[0104] At the time t=5, the sum (corresponding to β in the NumericalExpression (2)) of the absolute values of the differences between thefield image B2 at the time t=3 and the field image C2 at the time t=5 iscalculated. Since β has a value larger than the predetermined thresholdvalue, the frame structure analyzing means 104 outputs the controlsignal 115 similar to that outputted when the time=3 to the ratedoubling means 105. As a result, the rate doubling means 105 producesC1+C2 as one frame and outputs the frame.

[0105] At the time t=6 and thereafter, α and β are calculated in themanner described above and rate doubling is performed by the sameprocedure.

[0106] In general, if α or β calculated as the sum of the absolutevalues of the field differences at a time n (n is an integer) is largerthan a predetermined threshold value, one frame is produced from a fieldat the time n and a field at the time n+1 as a double rate output at thetime n and the same frame is outputted twice at the time n and at thetime n+1.

[0107] If α or β is smaller than the threshold value, on the other hand,an output at the immediately preceding time(output at a time (n−1)) isrepeatedly produced even at the time n.

[0108] In the present structure, each of the outputs at the times t=0,1, 2 is properly composed of the frame consisting of A1 and A2 sampledat the same time so that a double rate output free from image qualitydegradation is obtained. Moreover, each of the outputs at the subsequenttimes t=3, 4 can also be composed of the frame consisting of B1 and B2sampled at the same time so that a double rate output free from imagequality degradation is similarly obtained. Furthermore, the output atthe subsequent time t=5 can also be composed of the frame consisting ofC1 and C2 so that a double rate output free from image qualitydegradation is similarly obtained.

[0109] Thus, double rate conversion can be performed sequentially withrespect to a transmitted bitstream resulting from the MPEG2 encoding ofthe 24p material with the 60i signal without causing image qualitydegradation.

[0110] Although each of x, y in the (Numerical Expression 1), (NumericalExpression 2) has been calculated over the entire region of effectivepixels in the present embodiment, exactly the same effects can also beachieved by calculating instead the sum of the absolute values ofdifferences at a finite number of points. To determine the finite numberof points, there can be adopted a method of selecting points at randomas characteristic points or a method of determining a specified scanningline.

[0111] (Embodiment 2)

[0112] Below, a second embodiment of the present invention will bedescribed with reference to the drawings.

[0113]FIG. 4 is a block diagram showing the respective structures of areceiving apparatus and a transmitting apparatus as an embodiment of theprogressive image signal receiving apparatus according to the presentinvention.

[0114] For simplicity, the description will be given to the case where aprogressive signal at a rate of 60 frames per second is obtained from aprogressive signal at a rate of 24 frames per second, similarly to thefirst embodiment.

[0115] In FIG. 4, a reference numeral 401 denotes 24p/60i convertingmeans for converting a progressive signal having the rate of 24 framesper second for a film material or the like to a 60i signal having afield structure with a rate of 60 fields per second. A reference numeral402 denotes an MPEG2 video encoding means for producing a bitstream inaccordance with the description in ISO/IEC 13818-2. A reference numeral403 denotes an MPEG2 video decoding means for reconstructing the 60iimage signal at the rate of 60 fields/second from the aforesaidbitstream. The foregoing structure is the same as in the firstembodiment.

[0116] A reference numeral 404 denotes temporary storing means forreceiving an output of the MPEG2 video decoding means 403 and delayingthe current frame by a 1 frame time. A reference numeral 405 denotesjudging means for performing an operation between respective signalsrepresenting the current frame and the immediately preceding frame basedon the output of the MPEG2 video decoding means 403 and an output of thetemporary storing means 404. A reference numeral 406 denotes second ratedoubling means for receiving the output of the temporary storing means404 and an output of the judging means 405, adaptably selecting a ratedoubling method for the output signal from the temporary storing means404 based on the control signal from the aforesaid judging means 405,and outputting a double rate signal 416.

[0117] A reference numeral 410 denotes a 24p signal having a frame rateof 24 frames/second. A reference numeral 411 denotes a 60i signal havinga frame rate of 60 fields/second. A reference numeral 412 denotes abitstream defined in ISO/IEC 13818-2. A reference numeral 413 denotes a60i image signal having a frame rate of 60 fields/second. A referencenumeral 414 denotes a delayed image signal which has been delayed by a 1frame time. A reference numeral 415 denotes an output control signal forthe judging means. A reference numeral 416 denotes a 60p image signalhaving a doubled frame rate of 60 frames/second.

[0118] A description will be given to the operation of the progressivesignal transmitting/receiving apparatus thus structured.

[0119] First, the 24p/60i converter 401 produces the 60i signal 411 atthe rate of 60 fields/second from the material with the rate of 24frames per second in exactly the same manner as described in the firstembodiment and outputs the 60i signal 411 to the MPEG2 video encodingmeans 402. The 60i signal 411 is converted by the MPEG2 video encodingmeans 402 to the bitstream defined in ISO/IEC 13818-2, which forms thebitstream 412.

[0120] The bitstream 412 is subjected to arbitrary modulation anddemodulation and transmitted to reach the receiver via a transmissionpath. At the receiver, the bitstream 412 is inputted to the MPEG2 videodecoding means 403.

[0121] The MPEG2 video decoding means 403 reconstructs an image from thebitstream in accordance with the description in ISO/IEC 13818-2.

[0122] The temporary storing means 404 receives the result of decodingfrom the MPEG2 video decoding means 403 and outputs it after delaying itby a 1 frame time.

[0123] The judging means 405 calculates, for each of the fields, the sumof the absolute values of the differences between pixels at thecorresponding locations from the current 60i image signal 413 and thedelayed image signal 414 which is 1 frame time previous thereto. It isassumed that the numerical expressions for the calculation are the sameas shown in (Numerical Expression 1) and (Numerical Expression 2).

[0124] In other words, the judging means 405 notifies, via the controlsignal 415, the second rate doubling means 406 of whether or not theframe of concern contains a repeat field by calculating the differencebetween the current field and the field which is 1 frame time previousthereto in accordance with the Numerical Expressions 1 and 2 andperforming a comparison between the difference and a predeterminedthreshold value.

[0125] The second rate doubling means 406 operates in exactly the samemanner as the rate doubling means 105 according to the first embodimentso that it uses the control signal 415 from the judging means 405 toconvert the delayed image signal 414 to a double rate signal and outputthe 60p image signal 416.

[0126] Thus, even in the case where the MPEG2 video decoding means 403has the conventional structure incapable of calculating the sum of theabsolute values of the differences, the temporary storing means 404 andthe judging means 405 according to the present embodiment enables theobtention of a double rate output which does not cause the degradationof image quality in a sequence of frames.

[0127] Although the present second embodiment has used the (NumericalExpression 1) and (Numerical Expression 2) to calculate each of i, jover the entire region of effective pixels, similarly to the firstembodiment, exactly the same effects can also be achieved by calculatinginstead the sum of the absolute values of differences at a finite numberof points.

[0128] On the other hand, a control signal representing a changeoverbetween frames is needed as a trigger since the values should be clearedto 0 at the beginning of the frame in calculating α and β represented by(Numerical Expression 1) and (Numerical Expression 2). By contrast, ifthe 60i image signal 413 is transmitted in accordance with the REC656format defined by CCIR, the beginning of the frame can be judged withthe code defined in REC656 so that it is no more necessary to input anadditional control signal indicating the beginning of the frame.

[0129] (Embodiment 3)

[0130]FIG. 5 is a block diagram showing the respective structures of areceiving apparatus and a transmitting apparatus as an embodiment of theprogressive image signal receiving apparatus according to the presentinvention.

[0131] For simplicity, the present embodiment will describe, by way ofexample, the case where a progressive signal at a rate of 60 frames persecond is obtained from a progressive signal at a rate of 24 frames persecond.

[0132] In FIG. 5, a reference numeral 501 denotes 24p/60i convertingmeans for converting a 24p signal having the rate of 24 frames persecond for a film material or the like to a 60i signal having a fieldstructure with a rate of 60 fields per second. A reference numeral 502denotes second MPEG2 video encoding means for producing a bitstream of avideo signal in accordance with the description in ISO/IEC 13818-2. Areference numeral 503 denotes flag bit analyzing means for analyzing thecontent of a specific flag bit in the bitstream. A reference numeral 504denotes second MPEG2 video decoding means for selectively switching therate doubling method and reconstructing the image signal at the rate of60 frames/second from the bitstream based on the control signal from theflag bit analyzing means 503.

[0133] A reference numeral 510 denotes a progressive signal having aframe rate of 24 frames/second. A reference numeral 511 denotes a 60isignal having a frame rate of 60 fields/second. A reference numeral 512denotes a bitstream defined in ISO/IEC13818-2. A reference numeral 513denotes a control signal for notifying the second MPEG2 video decodingmeans 504 of a rate doubling method. A reference numeral 514 denotes a60p image signal having a frame rate of 60 frames/second.

[0134] A description will be given to the operation of the progressivesignal transmitting/receiving apparatus thus structured.

[0135] First, the a 24p/60i converter 501 produces a signal at the rateof 60 fields/second from the material with the rate of 24 frames persecond in exactly the same manner as in the description of theconventional technique.

[0136] Accordingly, the relationship between the 24p signal 510 as theinput signal and the produced 60i signal 511 at the rate of 60fields/second is exactly the same as the relationship between the inputimage and the output image shown in FIG. 16.

[0137] The 60i signal 511 is converted by the second MPEG2 videoencoding means 502 to a bitstream defined in ISO/IEC 13818-2, whichforms the bitstream 512.

[0138]FIG. 6 is a view for illustrating the structure of the bitstream512, which shows the picture_coding_extension defined in ISO/IEC13818-2. In FIG. 6 represented as a program function, each of the “rows”corresponds to a physical bit string. It can also be said that FIG. 6shows the state of the bitstream in terms of hardware.

[0139] In the present embodiment, the second MPEG2 encoding means 502receives the input 60i signal 511, detects a field that has beenrepeated internally of the input signal 511, and encodes a framecontaining the repeated field by assuming the repeat first_field bit inthe picture_coding_extension to be 1. Consequently, the input 60isignal, which is at the rate of 30 frames per second, is converted tothe bit string at the rate of only 24 frames per second, which isoutputted as the bitstream 512.

[0140] The bitstream 512 is transmitted via arbitrary modulation anddemodulation to reach the receiver via a transmission path. At thereceiver, the bitstream 512 is inputted to the second MPEG2 videodecoding means 504. The second MPEG2 video decoding means 504reconstructs the image from the bitstream in accordance with thedescription in ISO/IEC 13818-2.

[0141] The flag bit analyzing means 503 notifies, via the control signal513, the second MPEG2 video coding means 504 of whether or not the frameto be subsequently displayed is with the repeat_first_field flag.

[0142]FIG. 7 is a view for illustrating the operation of the secondMPEG2 decoding means 504.

[0143] In FIG. 7, the frames A, B, C, and D each reconstructed from thebitstream and accompanied by a reference numeral 514 a representrespective frame data transmitted at the times t=0, 1, 2, and 3 inaccordance with the format of ISO/IECI3818-2.

[0144] The value 1 or 0 accompanied by a reference numeral 601represents the value of the repeat first field in the bitstream 512 thataccompanies the corresponding frame.

[0145] The second MPEG2 decoding means 504 according to the presentembodiment is different from the MPEG2 decoding means 103 (see FIG. 1)according to the foregoing embodiment in that it receives the bitstream512 and directly produces the 60p image signal without producing the 60iimage signal.

[0146] That is, the second MPEG2 decoding means 503 is notified by theoutput control signal 513 from the flag bit analyzing means 503 ofwhether the repeat_first_field is 1 or 0. During display at the rate of60 frames/second, if the repeat_first_field in a frame is 1, the secondMPEG2 decoding means 504 repeatedly outputs the frame three times. Ifthe repeat_first_field in a frame is 0, the second MPEG2 decoding means504 operates to repeatedly output the frame twice.

[0147]FIG. 7 shows an example of the case where the repeat_first_fieldis added. FIG. 7 shows the case where the repeat_first_field flag ineach of the frames A and C is 1 and AAABBCCCDD is outputted at thattime.

[0148] The present structure allows the second MPEG2 decoding means 504to produce the 60p image signal at the rate of 60 frames/second, inwhich frames are interpolated in proper temporal order, from thebitstream encoded from the material with the rate of 24 frames/second.

[0149] (Embodiment 4)

[0150]FIG. 8 is a block diagram showing the respective structures of areceiving apparatus and a transmitting apparatus as an embodiment of theprogressive image signal receiving apparatus according to the presentinvention.

[0151] For simplicity, the present embodiment will describe, by way ofexample, the case where a progressive signal at a rate of 60 frames persecond is obtained from a progressive signal at a rate of 24 frames persecond.

[0152] In FIG. 8, a reference numeral 801 denotes 24p/60i convertingmeans for converting the progressive signal having the rate of 24 framesper second for a film material or the like to a 60i signal having afield structure with a rate of 60 fields per second. The 24p/60iconverting means 801 operates similarly to the 24p/60i converting means101 according to the first embodiment. A reference numeral 802 denotesthird MPEG2 video encoding means for producing a bitstream of a videosignal in accordance with the description in ISO/IEC 13818-2. Areference numeral 803 denotes second flat bit analyzing means foranalyzing the content of a specific flag bit in the bitstream. Areference numeral 804 denotes third MPEG2 video decoding means forselectively switching the rate doubling method and reconstructing theimage signal at the rate of 60 frames/second from the bitstream based onthe control signal from the second flag bit analyzing means 803.

[0153] A reference numeral 810 denotes a 60p signal having a frame rateof 24 frames/second. A reference numeral 811 denotes a 60i signal havinga frame rate of 60 fields/second.

[0154] A reference numeral 812 denotes a bitstream defined in ISO/IEC13818-2. A reference numeral 813 denotes a control signal for analyzinga specific bit in the bitstream and notifying the third MPEG2 videodecoding means 804 of a rate doubling method. A reference numeral 814denotes a 60p image signal having a frame rate of 60 frames/second.

[0155] A description will be given to the operation of the progressivesignal transmitting/receiving apparatus thus structured.

[0156] First, the 24p/60i converter 801 produces the signal at the rateof 60 fields/second from a material with the rate of 24 frames persecond in exactly the same manner as in the part dedicated to thedescription of the prior art.

[0157] Next, an output of the 24p/60i converting means 801 is inputtedto the third MPEG2 video encoding means 802.

[0158] In the present embodiment, the third MPEG2 encoding means 802receives the input 60i signal 811, detects a field that has beenrepeated internally of the 60i signal 811, and does not transmit theportion of the 60i signal 811 corresponding to the repeated field.

[0159]FIGS. 9 and 10 are views for illustrating the operation of thethird MPEG2 video encoding means 802 and the like according to thepresent embodiment, of which FIG. 9 shows a Sequence_header defined inISO/IEC 13818-2 and FIG. 10 shows a Sequence_extension defined inISO/IEC 13818-2.

[0160] In FIGS. 9 and 10 each represented as a program function, each ofthe “rows” corresponds to a physical bit string. It can also be saidthat each of FIGS. 9 and 10 shows the state of the bitstream in terms ofhardware, similarly to FIG. 6.

[0161] The third video encoding means 802 operates to construct abitstream by writing 1 in the frame_rate_code bit shown in FIG. 9 andwriting 1 in the progressive-sequence bit shown in FIG. 10.

[0162] Although the present embodiment does not use therepeat_first_field bit used in the third embodiment described above, asignal at the rate of 30 frames per second is eventually transmitted atthe rate of 24 frames per second.

[0163] The bitstream 812 is transmitted via arbitrary modulation anddemodulation to reach the receiver via a transmission path. At thereceiver, the bitstream 812 is inputted to the third MPEG2 videodecoding means 804.

[0164] The third MPEG2 video decoding means 804 reconstructs an imagefrom the bitstream in accordance with the description in ISO/IEC13818-2.

[0165] If the progressive_sequence flag bit shown in FIG. 10 is 1, thesecond flag bit analyzing means 803 calculates the number of times offrame repeats based on a ratio between the value described in theframe_rate_code and a frame rate to be displayed.

[0166] Since the present embodiment has considered the case where thematerial is a 24p signal, it is assumed that the frame_rate_code =2,which is defined in MPEG2 (ISO/IEC 13818-2) as a value indicating 24 Hz,has been added to the bitstream 812.

[0167] If the output frame rate of the receiving apparatus is assumed tobe 60 Hz, the ratio thereof to 24 Hz can be calculated to be 2:5.Accordingly, if a frame repeat is performed to construct 5 output framesrelative to 2 input frames, it is obvious that the input/output ratio ismaintained. Hence, the second flag bit analyzing means 803 notifies, viathe control signal 813, the third video decoding means 804 that a framerepeat be performed to maintain the input/output frame ratio.

[0168] Below, a detailed description will be given to the operation ofthe third MPEG2 video decoding means 804 with reference to FIG. 11.

[0169]FIG. 11 is a view for illustrating the operation of the thirdMPEG2 decoding means 804.

[0170] The third MPEG2 decoding means 804 performs a frame repeat basedon the output control signal 813 from the second flag bit analyzingmeans 803, as shown in FIG. 11, and produces an output.

[0171] In FIG. 11, the frames A, B, C, and D each reconstructed from thebitstream and accompanied by a reference numeral 814 a are respective24p image signals produced when images are reconstructed from thebitstream 812 transmitted at the times t=0, 1, 2, 3 in accordance withthe format of ISO/IEC 13818-2 within the video decoding means 804.

[0172] It is to be noted that, since the A, B, C, and D of the imagesignal 812 are constructed within the third video decoding means 804,they do not come out of the third video decoding means directly asexternal signals but form the 24p image signals when images areconstructed from the bitstream 812 in accordance with the ISO/IEC13818-2.

[0173] From the output of the second flag bit analyzing means 803, ithas been understood that the frequency of frame repeats is adjustedproperly if five output frames are produced relative to two inputframes. As a result, the third video decoding means 804 repeats each ofthe frames A and C three times and each of the frames B and D twice toeventually output the 60p-image signal, as indicated by the image signalaccompanied by the reference numeral 814 in FIG. 11.

[0174] The present structure allows the third MPEG2 decoding means 804to produce the 60p image signal output at the rate of 360 frames/second,in which frames are interpolated in proper temporal order, from thebitstream encoded from the material with the rate of 24 frames/second.

[0175] Although the present embodiment has described the case where onlythe frames A and C are repeated three times in the description of theoperation of the third video decoding means 804, another frame may alsobe repeated provided that the frequency of repeats is maintained at 2:5.In that case also, the 60p signal in correct order of display isobtained in exactly the same manner. In short, it is sufficient torepeat a frame such that a specified ratio is maintained between thenumber of input frames and the number of output frames irrespective ofthe frame to be repeated. Accordingly, exactly the same effects can beachieved if such an image signal as AABBBCCCDD is outputted by repeatingeach of the frames B and C three times.

[0176] Since the present invention is for performing double speedconversion with respect to a material which is progressive withoutimpairing the image quality thereof, considerations will be given onlyto the bitstream accompanied by the progressive_sequence=1 and atechnique used when the material has a field structure (in the casewhere progressive_sequence=0) will not be mentioned herein.

[0177] (Embodiment 5)

[0178]FIG. 8 is a block diagram showing the respective structures of areceiving apparatus and a transmitting apparatus as an embodiment of theprogressive image signal receiving apparatus according to the presentinvention.

[0179] The structure according to the present embodiment is the same asthe structure according to the foregoing fourth embodiment except forthe third MPEG2 encoding means 802. Specifically, the third MPEG2encoding means 802 according to the present embodiment uses a bit fieldof extension_and_user_data (0) defined in ISO/IEC 13818-2 shown in FIG.9, while the third MPEG2 encoding means 802 according to the foregoingembodiment adds 1 to each of the frame_rate_code flat bit and theprogressive_frame flag bit prior to transmission. The present embodimentwill also describe, by way of example, the case where a progressivesignal at the rate of 60 frames per second is obtained from aprogressive signal at the rate of 24 frames, similarly to the foregoing.

[0180]FIG. 12 is a view for illustrating a method of using theextension_and_user_data(0) in the present embodiment.

[0181] In FIG. 12 represented as a program function, each of the rowscorresponds to a physical bit string. It can also be said that FIG. 12shows the state of the bitstream in terms of hardware, similarly to FIG.6.

[0182] Since the user_data_start_code is 0×B2 in hexadeimal_notation asdefined in ISO/IEC 13818-2, data headed by 0×000001B2 herein forms userdata.

[0183]FIG. 13 is a view for illustrating the meaning of the 4-bit valueof the frame_code contained in FIG. 12.

[0184] In FIG. 13 represented as a program function, each of the rowscorresponds to a physical bit string. It can also be said that FIG. 13shows the state of the bitstream in terms of hardware, similarly to FIG.6.

[0185] If the frame_code is 0000 0001 in FIG. 13, for example, itexplicitly indicates that the material is an interlace signal at therate of 24 frames/second. Likewise, it is assumed that, if theframe_code is 0000 1000, it indicates a progressive signal at the rateof 23.976 frames/second.

[0186] If the material is a progressive signal having a frame rate of23.976 Hz, for example, the user data field becomes “0×00000B208”.

[0187] The bit string thus encoded by using theextension_and_user_data(0) field is subjected to necessary modulationand inputted to the third MPEG2 decoding means 804 and to the secondflag bit analyzing means 803 via a transmission system, similarly to thefourth embodiment.

[0188] The second flag bit analyzing means 803 calculates the frame rateratio not by using the frame_rate_code and the progressive_sequence butby judging from the content of the description of theextension_and_user_data (0). Except for this, the second flag bitanalyzing means 803 operates in exactly the same manner as in the fourthembodiment.

[0189] The third MPEG2 decoding means 804 receives the control signal813 from the second flag bit analyzing means 803 and produces an outputby performing frame repeats in the same manner as shown in, e.g., FIG.11.

[0190] The present structure allows the third MPEG2 decoding means 804to produce the 60p image signal, in which frames are interpolated inproper temporal order, at the rate of 60 frames/second from thebitstream encoded from the material at the rate of 24 frames/second.

[0191] Although the present embodiment has described the case where thebit representing the frame rate of the material is placed in theextension_and_user_data(0), it is not limited thereto. If user dataaccording to the extension-and-user-data(1) orextension_and_user_data(2) is used instead, exactly the same effects canbe achieved.

[0192] Thus, the progressive image signal transmitting/receivingapparatus according to the foregoing embodiments are structured to havethe MPEG2 video encoding means for converting an input image signal to abitstream defined in ISO/IEC 13818-2, the MEPG2 video decoding means forreconstructing the image signal from the aforesaid bitstream, the framestructure analyzing means for calculating an inter-frame difference froma frame image produced in the process of decoding operation performed bythe aforesaid MPEG2 video decoding means, and the rate doubling meansconnected to the aforesaid MPEG2 decoding means and to the framestructure analyzing means to perform rate doubling based on a controlsignal indicating the presence or absence of the inter-frame differencethat has been outputted from the frame structure analyzing means.

[0193] Alternatively, the progressive image signaltransmitting/receiving apparatus according to the foregoing embodimentsare structured to have the MPEG2 video encoding means for converting aninput image signal to a bitstream defined in ISO/IEC 13818-2, whilesimultaneously describing the frame structure of the material image andframe rate data at bit positions predetermined during transmission andreception, the MPEG2 video decoding means for reconstructing the imagesignal from the bitstream, the flag bit analyzing means for judgingwhether or not the frame is a frame to be repeated from thepredetermined bits in the MPEG2 bitstream, and the rate doubling meansconnected to the aforesaid MPEG2 decoding means and to the aforesaidflag bit analyzing means to double the scanning rate of the output ofthe MPEG2 video decoding means based on the control signal outputtedfrom the flag bit analyzing means.

[0194] With such structures, it is judged whether or not a specifiedframe decoded at the receiving apparatus is a frame to be repeatedlydisplayed and control operation is performed based on the judgment. Thisenables double rate display without causing the degradation of imagequality.

[0195] It is also possible to produce a recording medium such as amagnetic disk or an optical disk having a program recorded thereon forcausing all or a part of means of the signal transmitting apparatus orsignal receiving apparatus according to each of the foregoingembodiments to be implemented by a computer and cause the computer toperform the operations as described above. Such a structure achieves thesame effects as described above.

[0196] Although each of the foregoing embodiments has described the casewhere the video material has the progressive structure (24p) at the rateof 24 frames per second, which is represented by a film, and the outputimage is the video signal (60p) of progressive type at the rate of 60frames per second, it is not limited thereto. Similar effects can beachieved by exactly the same procedure in any other case where, e.g.,the video material is 25p, 48p, or 72p and the output side is 50p, 750p,or 1080p.

[0197] A brief description will be given to the respective structures ofthe receiving apparatus and the transmitting apparatus in the case wherethe material is 24p and the output side is 50p with reference to FIG. 1.In this case, the structures can easily be implemented by replacing the24p/60i converting means 101 with 24p/50i converting means for receivinga 24p signal, converting the input signal to a 50i signal, andoutputting the 50i signal and by performing the replacement of the MPEG2video decoding means 103, the rate doubling means 105, and the like withsimilar intention. After such replacements, therefore, an output of the24p/50i converting means is a 50i signal, an output of the MPEG2 videodecoding means is a 50i image signal, and an output of the rate doublingmeans 105 is a 50p image signal. Such structures achieve the sameeffects as achieved by the structure of FIG. 1.

[0198] FIGS. 14(a), 14(b), and 14(c) are views diagrammatically showingcorrespondences among the 24p signal, the 50i signal (PAL), and the 50psignal (PAL double rate signal) in this case. In the drawings, each ofthe frames A to L is repeated twice and the frame M is repeated threetime. Thereafter, the repetitions are performed twice and three times atthe same intervals.

[0199] In the drawings, each of A1 to N2 diagrammatically represents onefield image and the notation thereof is the same as in the cases shownin FIGS. 16, 17(a), 17(b), and the like. For example, the portionaccompanied by A1 is the first field (top field, odd field) of the frameA and the portion accompanied by A2 is the second field (bottom field,even field) of the frame A.

[0200] The same replacements as described above may also be performed inFIG. 4. In this case, the structures can easily be implemented byreplacing the 24p/60i converting means 401 with 24p/50i converting meansand performing the replacement of the MPEG2 video decoding means 403,the rate doubling means 405, and the like with similar intention. Aftersuch replacements, therefore, an output of the 24p/50i converting meansis a 50i signal, an output of the MPEG2 video decoding means is a 50iimage signal, and an output of the rate doubling means 105 is a 50pimage signal. Such structures achieve the same effects as achieved bythe structure of FIG. 4.

[0201] The same replacements as described above may also be performed inFIG. 5. In this case, the structures can easily be implemented byreplacing the 24p/60i converting means 501 with 24p/50i converting meansand performing the replacement of the second MPEG2 video decoding means504 and the like with similar intention. After such replacements,therefore, an output of the 24p/50i converting means is a 50i signal andan output of the second MPEG2 video decoding means is a 50p imagesignal. Such structures achieve the same effects as achieved by thestructure of FIG. 5.

[0202] Thus, according to the present embodiment, a repeated field canbe detected by calculating the difference in the decoded image even whendata on the material is not provided at the transmitter and optimum ratedoubling as stated previously can be performed by following anappropriate rate doubling procedure.

[0203] Moreover, optimum rate doubling conversion can be performed bydescribing the frame rate of the material at the transmitter,transmitting it to the receiver, and restoring the data at the receiver.

[0204] As is apparent from the foregoing description, the presentinvention has the advantage of producing a double rate signal superiorto that produced conventionally and maintaining vertical resolution evenwhen inter-field motion is dynamic.

INDUSTRIAL APPLICABILITY

[0205] As described above, the present invention provides theprogressive image signal transmitting apparatus, the progressive imagesignal receiving apparatus, and the medium each capable of producing adouble rate signal superior to that produced conventionally andmaintaining vertical resolution even when inter-field motion is dynamic.

What is claimed is:
 1. A progressive image signal receiving apparatuscomprising: video decoding means for receiving a bitstream, convertingthe bitstream to an interlaced video signal and outputting the videosignal; frame structure analyzing means for calculating, based onrespective signals representing a current frame and a frame which is 1frame time previous to the current frame each outputted from said videodecoding means, a difference between the both frame signals andoutputting a specified control signal based on a result of thecalculation; and rate doubling means for producing a frame signal basedon the video signal outputted from said video decoding means and on thecontrol signal outputted from said frame structure analyzing means toprovide a progressive signal at a scanning rate which is a specifiednumber of times as high as a scanning rate of the output signal fromsaid video decoding means.
 2. A progressive image signal receivingapparatus comprising: video decoding means for receiving a bitstream andoutputting an interlaced video signal; temporary storing means forreceiving the output signal from said video decoding means and delayingthe signal by a 1 frame time; judging means for calculating, based on acurrent signal outputted from said video decoding means and a previous-frame signal outputted from said temporary storing means, a differencebetween the both frame signals and outputting a specified control signalbased on a result of the calculation; and rate doubling means forproducing a frame signal based on the video signal outputted from saidtemporary storing means and on the control signal outputted from saidjudging means to provide a progressive signal at a scanning rate whichis a specified number of times as high as a scanning rate of the outputsignal from said temporary storing means.
 3. The progressive imagesignal receiving apparatus according to claim 1 or 2, wherein saidbitstream is a bitstream defined in ISO/IEC 13818-2.
 4. The progressiveimage signal receiving apparatus according to claim 1 or 2, wherein saidframe structure analyzing means calculates, in calculating thedifference between said both frame signals, the sum of the absolutevalues of differences between signals representing fields of the currentframe and signals representing fields of the previous framecorresponding to the signals representing the fields of the currentframe.
 5. The progressive image signal receiving apparatus according toclaim 1 or 2, wherein said frame structure analyzing means calculates,in calculating the difference between said both frame signals, the sumof the absolute values of differences between pixels in a part of thecurrent frame and pixels in a part of the previous frame.
 6. Aprogressive image signal receiving apparatus comprising: video decodingmeans for receiving a bitstream, converting the bitstream to a videosignal of progressive type, and outputting the video signal; and flagbit analyzing means for detecting, in said bitstream, a flag signalindicating the presence or absence of a field repeat describedcorrespondingly to a frame signal and outputting, to said video decodingmeans, the presence or absence of the field repeat indicated by thedetected flag signal, if said output from said flag bit analyzing meansindicates the presence of said field repeat, said video decoding meansrepeatedly outputting the same frame signal as the frame signalcorresponding to said flag signal and outputting said video signal ofprogressive type at a scanning rate which is a specified number of timesas high as a scanning rate of the frame signal in said bitstream.
 7. Aprogressive image signal transmitting apparatus for transmitting a videomaterial shot by a sequential scanning (progressive scanning) method inaccordance with a bitstream defined in ISO/IEC 13818-2, saidtransmitting apparatus describing a frame rate of said video material byusing a bit position in a user data region in said bitstream andtransmitting the frame rate.
 8. The progressive image signaltransmitting apparatus according to claim 7, wherein, when the bitposition in said user data region is used, an extension_and_user_data(0) bit field, an extension_and_user_data (1) bit field, or anextension_and_user_data (2) bit field is used.
 9. A progressive imagesignal receiving apparatus for receiving a bitstream transmitted from atransmitting apparatus and outputting a sequential scanning signal to aprogressive monitor, said receiving apparatus comprising: second flagbit analyzing means for recognizing a frame rate of a video materialfrom bit data at a given bit position predefined by agreement with saidtransmitting apparatus; and video decoding means for receiving an outputof said second flag bit analyzing means and said bitstream, determiningthe frequency of frame repeats based on a ratio between the output ofsaid second flag bit analyzing means and a frame rate displayed on saidprogressive monitor, reconstructing an image, and outputting aprogressive signal.
 10. The progressive image signal receiving apparatusaccording to claim 10, wherein said bitstream transmitted is a bitstreamdefined in ISO/IEC 13818-2.
 11. The progressive image signal receivingapparatus according to claim 10, wherein said second flag bit analyzingmeans recognizes said frame rate from an extension_and_user_data (0) bitfield, an extension_and_user_data (1) bit field, or anextension_and_user_data (2) bit field in said bitstream defined inISO/IEC 13818-2.
 12. A progressive image signal receiving apparatus forreceiving a bitstream defined in ISO/IEC 13818-2 and outputting aprogressive signal, said receiving apparatus comprising: flag bitanalyzing means for analyzing whether or not a code value described in aframe_rate_code flag in a sequence_header is half the value of a framerate of said progressive signal outputted and outputting a result of theanalysis as a control signal; video decoding means for receiving saidbitstream and reconstructing an image based on said definition inISO/IEC 13818-2; and rate doubling means for converting, based on saidcontrol signal outputted from said flag bit analyzing means, an outputsignal from said video decoding means to a signal at a scanning ratewhich is double the scanning rate of the output signal.
 13. A mediumhaving a program recorded thereon for causing all or a part of means ofa progressive image signal transmitting apparatus as recited in claim 7or 8 to be implemented by a computer.
 14. A medium having a programcontaining thereon for causing all or a part of means of a progressiveimage signal receiving apparatus as recited in claim 1, 2, 3, 4, 5, 6,9, 10, 11, or 12 to be implemented by a computer.